... and on a slightly related note, I've now noticed I have osh_updated_by_functions.php in MY_STORE/includes/functions/extra_functions

That's one of your files @lat9, not really sure how it got there other than it seems part of your Orders Status History mod. I couldn't find the file in any of my plugin archives and had to resort to Google to find out what it was.

I don't know if it's being used by my site, I trust it's ok for me to delete it?